Various optically switchable devices are available for controlling tinting, reflectivity, etc. of window panes. Electrochromic devices are one example of optically switchable devices generally. Electrochromism is a phenomenon in which a material exhibits a reversible electrochemically-mediated change in an optical property when placed in a different electronic state, typically by being subjected to a voltage change. The optical property being manipulated is typically one or more of color, transmittance, absorbance, and reflectance. One well known electrochromic material is tungsten oxide (WO3). Tungsten oxide is a cathodic electrochromic material in which a coloration transition, transparent to blue, occurs by electrochemical reduction.
Electrochromic materials may be incorporated into, for example, windows for home, commercial, and other uses. The color, transmittance, absorbance, and/or reflectance of such windows may be changed by inducing a change in the electrochromic material, that is, electrochromic windows are windows that can be darkened or lightened electronically. A small voltage applied to an electrochromic device of the window will cause it to darken; reversing the voltage causes it to lighten. This capability allows for control of the amount of light that passes through the window, and presents an enormous opportunity for electrochromic windows to be used not only for aesthetic purposes but also for energy-savings.
With energy conservation being of foremost concern in modern energy policy, it is expected that growth of the electrochromic window industry will be robust in the coming years. An important aspect of electrochromic window fabrication is coating of thin films on glass to produce an electrochromic device stack, and patterning the device stack to make it functional. Part of the patterning process includes removing portions of the device stack to reveal underlying transparent conductive oxide (TCO) in order to fabricate electrical connections, e.g. bus bars, onto the exposed lower TCO and the upper TCO, in order to deliver electricity to them and thus impart a potential across the electrochromic device stack to drive its coloring function. Selectively removing these materials to reveal the underlying TCO may be problematic, e.g., depending upon the materials that make up the electrochromic device.